Thought experiment

Sun at your back. Rain ahead. Each drop refracts white light, reflects once inside, and sends color out again. The bright arc is a cone of rays. You stand at the anti-solar point. The primary bow gathers near forty-two degrees from that axis. Move, and the bow moves with you. Same law. New meeting.

Nature answers a geometric question: at what angle does the light return to an eye that is looking? Wheeler’s bit lives in that yes of minimum deviation.